It has long been desired to develop an efficient and economical process for the manufacture of N-monosubstituted p-phenylenediamines. These materials are particularly useful for the manufacture of antioxidants and antiozonants for use in rubber products and as intermediates for the preparation of dyes.
Conventionally, these materials have been prepared by the hydrogenation of nitrosoarylamines as a salt of an alkali metal in an aqueous system. Reduction is typically performed using gaseous hydrogen in the presence of a conventional hydrogenation catalyst. An example of this process is shown in U.S. Pat. No. 2,974,169.
In later work, such as described in U.S. Pat. No. 4,313,002, the alkaline metal salts are reduced in other solvent systems such as aromatic hydrocarbons and saturated aliphatic alcohols. Still the hydrogenation step is taught to be performed using hydrogen over a conventional hydrogenation catalyst.
These processes suffer from the disadvantage of utilizing hydrogenation catalysts which are typically very costly noble metal catalysts such as, for example, platinum and palladium.
U.S. Pat. No. 4,448,994 teaches the use of a reducing sugar to reduce an alkaline metal salt of a nitrosoamine in an aqueous solution. This process suffers from the typical problems associated with aqueous solutions of these salts in that they tend to hydrolyze and, therefore, are unstable upon storage.
In U.S. Pat. No. 4,479,008, it is disclosed that a diphenylamine can be N-nitrosated; rearranged to form 4-nitrosodiphenylamine and subsequently hydrogenated over a conventional 5% palladium on carbon catalyst with a hydrogen pressure of 500 -800 psi at 80.degree. C. by using an aliphatic alcohol as a medium for all of the foregoing steps. This disclosure teaches the necessity of utilizing the noble metal catalysts of the prior art for the reduction step which, as noted above, are extremely expensive.